Method for controlling a robot arm, and robot for implementing the method

1. A method for controlling a robot arm for use in medical or industrial applications, wherein a robot arm ( 10 ) with a redundant number of joints is used wherein at least a first and a second joint ( 12 a , 12 b ) are controlled and wherein the redundancy of joints is used to optimize a quality criterion, to align two zero moment controlled axes substantially vertical to the instrument axis, an instrument connected to said robot arm is passed through an opening ( 19 ), a torque acting in at least one joint ( 12 ) is detected, the interaction torque acting in said joint ( 12 ) is controlled to substantially zero by means of a control device in order to reduce the forces acting on the edge of the opening, the control of at least a first joint ( 12 a ), which due to its position in space can generate a force in the plane parallel to the patient, is performed such that the force is substantially zero at the patient penetration point, and joint axes ( 20 a , 20 b ) of said first and second joints are vertical to each other, and the instrument axis ( 18 ) vertical to both joint axes ( 20 a , 20 b ) and includes an angle other than zero with the joint axes.

2. The method of claim 1 , wherein the control using the control device is performed when predetermined limit values are exceeded or under-run.

3. The method of claim 1 , wherein the control is effected using a zero moment control.

4. The method of claim 1 , wherein the joints ( 12 a , 12 b ) connected with a joint connecting element ( 16 ) that is closest to the element of the environment are controlled.

5. The method claim 1 , wherein correction terms are included in the control to compensate for moments and/or forces caused by inertia and/or friction.

6. The method of claim 1 , wherein the control of the robot arm is supported by a haptic flow of information.

7. The method of claim 1 , wherein at least one of the joints controlled is adapted to be switched to a controlled free movement.

8. The method of claim 1 , wherein, due to the redundant number of joints, a change of position of at least one connecting element ( 16 ) is possible through haptic interaction without changing the position of the end effector, the forces acting on the edge of the opening being substantially zero.

9. The method of claim 1 , wherein the optimized quality criterion is alignment of the two zero moment controlled axes substantially vertical to the instrument axis.

10. A robot, for use in medical applications, comprising a robot arm ( 10 ) with a plurality of joints ( 12 ), the number of joints being redundant, connecting elements ( 16 ) being arranged between the joints ( 12 ), an end effector, and actuators and torque sensors ( 14 , 22 ) connected with the joints ( 12 ) and/or the connecting elements ( 15 ), wherein a first and a second joint ( 12 a , 12 b ) are connected with a connecting element ( 16 ) and the first and second joints ( 12 a , 12 b ) are arranged closest to an element of the environment and a control device, connected with the torque sensors ( 14 , 22 ) and the actuators, for executing the method of claim 1 wherein said first joint ( 12 a ), a joint closest to the element of the environment, includes a torque sensor ( 14 , 22 ) wherein the torque sensor is an internal torque sensor ( 14 ) integrated in the joint and/or a torque sensor ( 22 ) connected with the adjacent connecting element ( 16 ).

11. The method of claim 3 wherein the control is effected using an impedance control.

12. The method of claim 3 wherein the control is effected using an admittance control.

13. The method of claim 3 wherein the control is effected using an impedance projection.